1. Field of the Invention
The present invention relates to a method used for an induction type power supply system, and more particularly, to a method of detecting whether there is an intruding metal existing in a power transmission range of an induction type power supply system.
2. Description of the Prior Art
An induction type power supply system includes a power supplying terminal and a power receiving terminal. The power supplying terminal applies a driver circuit to drive a supplying-end coil to generate resonance, in order to send electromagnetic waves. A coil of the power receiving terminal may receive the electromagnetic waves and perform power conversion to generate DC power to be supplied for a device in the power receiving terminal. In general, both sides of the coil are capable of transmitting and receiving electromagnetic waves; hence, a magnetic material is always disposed on the non-induction side of the coil, allowing the electromagnetic energy to be aggregated on the induction side. The magnetic material close to the coil may enlarge the coil inductance, and thereby increase the electromagnetic induction capability. In addition, the electromagnetic energy exerted on a metal may heat the metal. This principle is similar to an induction cooker. Therefore, another function of the magnetic material is to isolate the electromagnetic energy, in order to prevent the electromagnetic energy from interfering with the operations of the device behind the coil, and also prevent the electromagnetic energy from heating surrounding metals for safety.
In the induction type power supply system, an induction coil is included in each of the power supplying terminal and the power receiving terminal for sending power energy and control signals. The safety issue should be considered in this system. However, a user may intentionally or unintentionally insert a metal between these induction coils when using the induction type power supply system. If an intruding metal appears during power transmission, the electromagnetic energy generated by the coil may rapidly heat the intruding metal and cause an accident such as burning or exploding. Therefore, the industry pays much attention to this safety issue, and related products should have the capability of detecting whether an intruding metal exists. When there exists an intruding metal, power supply output may be cut off for protection.
In the prior art, a power loss is calculated by measuring the output power of the power supplying terminal and the input power of the power receiving terminal, and existence of the intruding metal is determined based on the calculated power loss and a predetermined threshold value. If the power loss exceeds the threshold value, the system may determine that there is an intruding metal. However, the above method of determining the intruding metal may not achieve satisfactory protection effects. For example, when a smaller intruding metal such as a coin, key or paper clip exists in the power transmission region of the power supplying terminal, the small intruding metal may not be successfully detected by the above method. Also, if the threshold value for determination is too strict, small noise interferences may be wrongly determined to be an intruding metal, which results in unnecessary power cut. Thus, there is a need for improvement over the prior art.